Hetero ring-containing disazo dyes have excellent fastness properties to light and particularly show a high molar absorption coefficient and a large color value, and hence they have been noted as disperse dyes of navy color for polyester fibers.
Many reports have already been made as to the process for preparing the hetero ring-containing disazo dyes (for example, Japanese Patent Application (OPI) Nos. 41734/76 and 33225/78 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application")), but conventional processes difficultly provide the dyes in satisfactorily high yield with, particularly, high purity.